Many different types of wireless access technologies have been developed including global standards for mobile communication (GSM), universal mobile telecommunication system (UMTS), CDMA2000, IEEE 802.16 wireless broadband (WiBro), WiFi and WiMAX, and IEEE 802.11 wireless local area network (WLAN). Each of these systems have been developed and tailored to provide specific applications.
With the pervasive adoption of wireless communication networks in enterprise, residential and public domains, continuous connectivity can be supported as the users of such networks move from one network to the other. With the emerging “always-on” life style, wireless transmit/receive units (WTRUs), (i.e., mobile stations (MS)), are required to support multiple heterogeneous networks, and multimode WTRUs that incorporate more than one of these wireless interfaces require an ability to seamlessly switch among them during communication.
IEEE 802.21 media independent handover (MIH) has been developed to enable a seamless handover based on measurements and triggers supplied from link layers. IEEE 802.21 defines media independent event service (ES), command service (CS) and information service (IS). IEEE 802.21 also defines media dependant/independent service access points (SAPs) and associated primitives for each specific access technology.
IEEE 802.21 MIH event and information service (EIS) requires MAC or physical layer-based event notification for link status updates between a WTRU and an MIH point of service (PoS). The MIH EIS events include link up, link down, link parameters change, link going down, service data unit (SDU) transmission status, link event rollback, pre trigger (L2 handoff imminent), and the like. Currently, link layer extensions required to support MIH EIS are under consideration for various technologies.
The key functionality provided by MIH is communication among the various wireless layers including an Internet protocol (IP) layer. The required messages are relayed by an MIH entity that is located in the protocol stack between the layer 2 and layer 3. The MIH entity may communicate with various IP protocol layers including a session initiation protocol (SIP) for signaling and a mobile IP layer for mobility management.
When a session is handed off from one access point to another using the same technology, the handover can usually be performed within that wireless technology itself without involving the MIH entity. For instance, a voice over IP (VoIP) call from a WiBro handset to a WiBro access point can be handed over to another WiBro access point within the same network using the same WiBro standard. However, to perform a handover from a WiBro access point to a UMTS network, the MIH would be required, since the two access points cannot communicate with each other at the link layer, and are in general on different IP subnets.
Accordingly, it would be desirable to provide a method and apparatus for performing handover between an IEEE 802.16 WiBro network and a UMTS network.